Phospatidylinositol 3-kinase (PI3K) is a ubiquitous lipid kinase involved in receptor signal transduction by tyrosine kinase receptors. PI3K comprises a large and complex family that includes 3 classes with multiple subunits and isoforms. The class I PI3Ks are composed of a Src homology-2 domain containing an 85 kDa regulatory subunit (p85) and a 100-kDa catalytic subunit (p110), which catalyses the phosphorylation of phosphoinositol 4-phosphate and phosphoinositol 4,5-phosphate at their D3 positions. The PI3K regulatory subunits include p85alpha and its truncated splice variants p50alpha and p55alpha, as well as p85beta and p55gamma; the catalytic subunits include p110alpha, p110beta, and p110delta. The human catalytic subunit p110alpha is encoded by the PIK3CA gene, located on the human chromosome 3 [Chr 3: 180.35-180.44 M bp] specifically [chr3:180,349,005-180,435,191 bp](NCBI reference sequence annotation) (3q26.3), which is frequently mutated in a variety of human cancers; PIK3CA has been shown to be mutated in 32% of colorectal cancers, 27% of glioblastomas, 25% of gastric cancers, 36% of hepatocellular carcinomas, 18-40% of breast cancers, 4-12% of ovarian cancers and 4% of lung cancers (Samuels et al., 2006). Most of these mutations map to three mutational hot-spots within the PIK3CA coding sequence, which are E542K, E545K and H1047R (Kang et al., 2005).
PI3K has been indicated in a wide range of cancers, such as colorectal carcinoma, where it is has been shown that the activation of PI3K/Akt is associated with colorectal carcinoma and can convert differentiated human gastric or colonic carcinoma cells to a less differentiated and more malignant phenotype (Rychahou et al 2006).
The effects of PI3K on tumor growth and progression are thought to be mediated by Aid, a downstream effector of PI3K. In humans there are three members of the Akt gene family, Akt 1, Akt 2 and Akt3. Aid is over expressed in a number of cancers, including colon, pancreatic, ovarian and some steroid hormone-insensitive breast cancers.
Inhibitors of proteins that are involved in the PI3K/Akt signalling, which have been suggested as potential therapeutic agents, include both siRNAs and antisense oligonucleotides (US2006/030536A), however to date most research in this area appears to have focused on the use of siRNAs.
WO2005/091849 describes antisense down-regulation of PI3K, however no specific antisense oligonucleotides are disclosed.
Zhang et al., 2004 (Cancer Biology and Therapy 3:12 1283-1289) discloses siRNAs targeting p110alpha and suggests its use in gene therapy in ovarian cancer.
Rychahou et al 2006 (Annals of Surgery 243833-844) discloses siRNA complexes targeting p85alpha and p110alpha which were found to decrease in vitro colon cancer cell survival and to increase apoptosis in human colon cancer cells, and decreased liver metastasis in in vivo experiments.
Meng et al., 2006 (Cellular Signalling 18 2262-2271) discloses siRNAs targeting p110alpha for inhibiting PI3K activity in ovarian cancer cells. The authors determined that inhibition of AKT 1 is sufficient to affect cell migration, invasion and proliferation.
Hsieh et al., 2004 (NAR 32 893-901) reports on the use of 148 siRNA duplexes targeting 30 genes within the PI3K pathway.
US 2005/0272682 discloses siRNA complexes targeting a phosphoinositide 3-kinase (PI3K) signal transduction pathway.
In certain embodiments, the invention provides highly efficient antisense oligonucleotides which target the PI3K pathway, specifically the PIK3CA mRNA, and in particular a new class of PIK3CA antagonists which have been selected based on the use of LNA chemistry, and/or by the selection of particularly effective target sites on the PIK3CA mRNA.